diff --git a/usr.bin/diff/diff.h b/usr.bin/diff/diff.h
index 4bea23db1ab..fe41e8746f4 100644
--- a/usr.bin/diff/diff.h
+++ b/usr.bin/diff/diff.h
@@ -1,6 +1,8 @@
 /*	$OpenBSD: diff.h,v 1.34 2020/11/01 18:16:08 jcs Exp $	*/
 
 /*-
+ * SPDX-License-Identifier: BSD-3-Clause
+ *
  * Copyright (c) 1991, 1993
  *	The Regents of the University of California.  All rights reserved.
  *